1. Field of the Invention
The present invention relates to an imaging capture method and apparatus, and more particularly to a method and apparatus for image capturing that is capable of capturing an image with a reduced current consumption.
2. Discussion of the Background
In recent years, imaging capture apparatuses such as digital cameras, for example, have been developed and become popular. The digital camera converts an optical image to electric image data and digitally records the image data on a storage medium. When the image is reproduced, the recorded digital data is retrieved from the storage medium and displayed on a display device or printed out as a hard copy image.
Referring initially to FIG. 1, a background digital camera 25 generally includes an optical lens 1, a mechanical shutter 2, an image optical pick-up element 3, a sample/hold circuit 5, an A/D (analog-to-digital) converter 6, a shutter drive circuit 7, a timing generating device 8, an image data controller 10, a system controller 11, a DRAM (dynamic random access memory) 12, an image display device 13, an image compression circuit 14, an image recording media 15, an EEPROM 16, and a manipulation switch 17.
The optical lens 1 focuses light rays onto a light receiving surface. The optical lens 1 is shown on the left side of FIG. 1. The mechanical shutter 2 controls incident rays of a light image. The optical pick-up element 3 includes photo-optic cells capable of converting the light rays received from the optical lens 1 into representative analog signals. Most commonly, the photo-optic cells take the form of Charge-Coupled Devices (CCDs).
The sample/hold circuit 5 extracts data corresponding to pixels of the image signals that are input from the image optical pick-up elements 3. The A/D converter 6 converts the representative analog signals into the digital signals representative of the image. The shutter drive circuit 7 provides shutter drive signals to the mechanical shutter 2.
The time generating device 8 supplies a synchronous signal to each of the optical pick-up elements 3, the sample/hold circuit 5, the A/L) converter 6, and the image data controller 10.
The image data controller 10 performs various operations such as an image processing including pixel interpolation, gamma compensation, gradation compensation image display signal conversion, and storage signal conversion. The system controller 11 controls the entire system associated with an operation of the digital camera. The DRAM 12 allows various image data to be temporary written and read when necessary. The image display device 13 displays a monitoring image during an operation associated with image processing and also displays captured images.
The image compression circuit 14 receives the appropriately formatted digital signals. The image compression circuit 14 operates to digitally compress the received digital images to reduce the amount of resources required to further process the digital signals. One such formatting scheme referred to as JPEG is commonly used, although there are a wide variety of suitable picture formats. The image recording media 15 includes a memory card for storing the image data of a captured image. The manipulation switch 17 provides manual input according to an order from an operator.
Referring now to FIG. 2, the image optical pick-up elements 3 of FIG. 1 take the form of interlines. Photodiodes 23 are arranged in a matrix with eight rows and four columns. Color filters R, G, and B are attached to the respective photodiodes 23 that respectively form pixel components, in accordance with a Bayer arrangement. Each of four vertical registers 20 is arranged to receive electric charges from the corresponding photodiodes aligned in a horizontal line and to transfer the received charges downwards. A horizontal register 21 is arranged to transfer the charges received from the four vertical registers 20. An output amplifier 22 that amplifies output signals is connected to an output side of the horizontal register 21.
Referring now to FIG. 3, an exemplary relationship is shown of various signals produced in the background digital camera 25. As shown in FIG. 3, a vertical synchronous signal VD sets a unit time to obtain one page of image data. Based on the photometric data of an object, an output duration in which a sub-pulse SUB is output is set and is controlled by the system controller 11. The mechanical shutter 2 is made to be opened by the shutter drive circuit 7, which operates upon an instruction of the system controller 11. An electric shutter operation for the image optical pick-up element 3 is performed during the time in which the sub-pulse SUB suspends outputting by a control signal supplied by the timing generating device 8. An exposure time of the image optical pick-up elements 3 that perform a shutter operation to the photodiode 23 is controlled by a discrete value of the sub-pulse SUB. During the exposure time, the electric charges are stored in the photodiodes 23. The electric charges stored in the above-described process are sequentially read by the vertical register 20 by placing a predetermined plus voltage to a vertical transfer electrode (not shown). The electric charges are transferred in the vertical direction by electric charges aligned in a unit of one horizontal line to the horizontal register 21. The electric charges are transferred along the horizontal register 21 and are output from the amplifier 32 (i.e., a CCD OUT in FIG. 3)
In FIG. 3, a recording trigger Tr for an image recording is produced upon a depressing of a release switch (not shown) in the monitoring mode. When the recording trigger Tr is produced, a shutter pulse is output by the shutter driving circuit 7 after the time the sub-pulse SUB is output under a control of the system controller 11 during a unit time corresponding to the vertical synchronous signal VD immediately following the recording trigger Tr. The shutter pulse is output before a time the mechanical shutter 2 is closed by a response time tm. After the lapse of the time point tm, the mechanical shutter 2 is closed and the exposure ends.
When the image optical pick-up elements 3 are interline-type CCDs, the electric charges are read from the photodiode 23 to the vertical register 20 in two or more fields. However, before the electric charges are transferred to the vertical register 20, unnecessary charges such as dark currents or smear components, in the vertical register 20, for example, are swept rapidly.
In this case, as shown in FIG. 3, image data are read twice, that is, from an odd number field and an even number field. There is a time Tp in which the above-described unnecessary charges are swept rapidly before transferring the electric charges to the vertical register 20. In a unit of time after the electric charges of the even number field are transferred, the shutter pulse begins to be output, the mechanical shutter 2 is opened, and monitoring begins.
As described above, imaging signals output from the image optical pick-up elements 3 are subject to a noise control by a correlation duplex sampling in the sample/hold circuit 5 and R, G, and B signals output from each of pixels are sampled and held, then undergo an A/D conversion by an integral multiple of the sub-carrier frequency of the NTSC signal, for example, by the A/D conversion circuit 6, and are then input to the image data controller 10. The R, G, and B signals to be input to the image data controller 10 are stored in the DRAM 12. Then, signal processing such as a white-balance calibration and a gamma processing, for example, are performed for the R, G, and B signals read from the DRAM 12 and luminance signals Y and color-difference signals Cr and Cb are created and stored in the DRAM 12.
To display an image of the object by the image display device 13, the image of the object is displayed in the image display device 13 based on the luminance signal Y and the color-difference signal that are read under control of the image data controller 10.
When the image of the object is stored in the image recording media 15 such as a memory card, for example, under the control of the image data controller 10, the luminance signals Y and the color-difference signals Cr and Cb are compressed in a predetermined format by the image compression circuit 14 and the compressed data are stored in the image media 15.
Furthermore, when image data stored in the image media 15 are reproduced, under the control of the image data controller 10, the image data read from the image media 15 are decompressed by the image compression circuit 14 and are displayed as an image of the object in the image display device 13.
The structure and function of the background digital camera is explained so far. However, unfortunately, the above-described background digital camera has a limitation in which because electric charges are sequentially transferred in the vertical register more rapidly than a normal electric charge reading in the rapid sweep of unnecessary electric charges such as dark current components or smear components, that thereby increases the current consumption. When the mechanical shutter is in operation, a shutter pulse needs to be kept being output for a predetermined period to maintain a shutter operation, resulting in more current consumption.